Capacitors are circuit elements that store electrical energy by keeping electric charge in an electric field. The capacitors are used with the characteristics of storing input electricity as electric memories. Capacitors have became essential electrical elements for applications in numerous electric circuits. Electric circuits usually utilize a great number and various type of capacitors, especially the circuits associated with frequency domain signal or AC signals power supply device and filtering circuits. In the decades, wireless communication through digital and analog signals has been developed progressively to make the whole world an earth village. Capacitors applied in filtering circuits, power supply, and wireless communication device and circuits are vital elements, with the critical specifications on the performance of capacitors.
Without limiting the scope of the invention, the background of the present invention illustrates a capacitor utilized and formed on a semiconductor substrate in general. Referring to FIG. 1, a prior art capacitor 10 is former on a semiconductor substrate 12 in partial cross section view. A first storage electrode 14 is formed on the substrate 12 by depositing and patterning a conductive layer. An ion implantation to a region on the substrate for forming a conductive area can also be utilized in forming the first storage electrode. A dielectric layer 16 is then formed above the first storage electrode 18. The dielectric layer 16 having high permittivity, such as silicon dioxide and silicon nitride, is formed by performing a chemical vapor deposition (CVD), a lithography, and an etching process. Finally, series of processes including physical vapor deposition, lithography, and etching are employed in forming a second storage electrode 18 above the dielectric layer 16, fabricating the capacitor 10 mentioned above. A planar capacitor with a fixed capacitance is finished in the semiconductor manufacturing processes.
Numerous capacitors are applied in filtering circuits, power supplying devices, and wireless communication circuits. The capacitors serve as vital elements with the critical specifications on their accuracy and performance. The application of capacitors can be divided as two kinds, the variable capacitance capacitors and the fixed capacitance capacitors. The variable capacitance capacitors are widely utilized in filtering circuits and power supplying devices. Conventional semiconductor manufacturing processes are unable to form a variable capacitor within the integrated circuits. Thus an integrated circuits must connect with the additional variable capacitor devices for filtering circuits and power supply applications. The additional variable capacitor devices not only increase the size of the whole circuits but also bring a problem of instability under electromagnetic noise.
Fixed capacitance capacitors are employed in numerous circuits with a specification on accurate capacitance. With higher integration in integrated circuits, each electrical element is reduced to the minimum and optimum scale of lithography in size. In such a scale, a high accuracy in size of pattern is hard to achieve on the semiconductor with present lithography and etching process. Thus the deviation in the accuracy of the capacitance are very frequent for a semiconductor manufacturing process. An accurate capacitance must be obtained through combining a number of capacitors connecting in parallel. In order to meet the requirements for applications in wireless communication device and circuits. In addition, the exact capacitance of each capacitor is unexpected before it is finished with semiconductor processes. The exact capacitance is measured by probing on the wafer of the semiconductor. At that time, the capacitance is already fixed and no more modification or tuning is possible. Connecting capacitors in parallel for obtaining specified capacitance further complicates the circuits. The connections also exploits more elements and needs more space on a wafer. Time wasted with above efforts leads to inefficiency and raises the manufacturing cost with the complicate circuits.